Thanks to global warming, extreme rainfall may be more common

Ken Bradley is research and policy center director at Environment Minnesota, which describes itself as a "statewide, citizen-based environmental advocacy organization."

Global warming is already beginning to affect life here in Minnesota, across America, and around the world. The first half of 2012 was the hottest January through July on record for the lower 48 states. Much of the country is suffering through prolonged drought. Species are on the move. Glaciers are melting while many political leaders are continuing to deny the indisputable science.

Roughly one month after the extreme downpour that hit Duluth and other communities in Minnesota, causing $100 million in damages, Environment Minnesota Research and Policy Center released a new report that documents one more way global warming is affecting our lives — an increase in the frequency and intensity of extreme rainstorms.

Our report, entitled "When It Rains, It Pours," found that storms with heavy rain are happening 30 percent more frequently in Minnesota now than they were 65 years ago. In other words, an extreme rainstorm that used to hit Minnesota once every 12 months on average now occurs every 9.2 months on average.

Scientists tell us that the trend toward heavier rainstorms is clearly linked to global warming, as warming increases evaporation and enables the air to hold more water, providing more fuel for these heavier rainstorms.

The implications of more frequent extreme rainstorms are serious. In the 20th century, flooding caused more property damage and loss of life in the United States than any other type of natural disaster. More frequent downpours will leave Minnesota even more vulnerable to dangerous flooding in years to come.

With more than half the United States suffering through one of the worst droughts in history, it's important to understand that bigger rainstorms happening more often does not mean more water will be available for us. Scientists actually predict that as global warming intensifies, longer periods of relative dryness will mark the periods between extreme rainstorms, increasing the risk of drought. This is because the same increased evaporation that leads to more water in the air also leads to drier soils.

In our report, we examined trends in the frequency of large rain and snow events across Minnesota and the United States, using data from weather stations nationwide and a methodology originally developed by scientists at the National Climatic Data Center and the Illinois State Water Survey.

We looked at daily rainfall and snowfall records from 1948 to 2011, identified the largest storms at each weather station, and analyzed when those storms occurred and how much precipitation fell with each.

Another key finding of our report is that the biggest rainstorms are getting bigger. The amount of precipitation released by the largest annual storms in Minnesota increased by 12 percent from 1948 to 2011.

While scientists predict that the trend toward more storms with extreme precipitation will only intensify as a result of global warming, there are actions we can take to minimize the danger.

Scientists tell us that we have very little time in which to prevent the worst effects of global warming — and a great deal of work to do. The good news is that the pollution reductions called for by scientists are achievable, and we already have started putting some of the most important pollution-reduction strategies to work.

At the federal level, the Obama administration has proposed carbon-pollution and fuel-efficiency standards for new cars and trucks through 2025, as well as carbon-pollution standards for new power plants. Vehicles and power plants are the two largest sources of carbon pollution, so getting these proposed standards finalized and on the books this year is critical to tackling global warming.

While these are important steps, we need to do much more at the state, local and federal levels if we expect future generations not to judge us as neglectful, delinquent stewards of our nation.

Now is the time for us to come together to solve this challenging problem and embrace solutions that will leave our planet better for generations to come.

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